This invention relates to retractable roofs, and is particularly relevant to large-scale retractable roofs of the type employed to cover the centre of a stadium such as an athletics or football stadium.
Given the cost of building large stadia there has been an interest in recent years in providing stadia which can be a venue for many different uses, not only simply for a single sport or type of event. In addition, there has been created a need for stadia which can be used throughout the year, regardless of weather conditions, and at any time, day or night. This has produced an increasing need for stadia which have roofs which can be moved so that a stadium can provide a traditional outdoor venue, but can still be used under adverse weather conditions and/or when temperatures drop at night, without affecting the comfort of the users of the stadium.
In recent time there have been proposed, and, indeed, built, many stadia with such roofs. There are difficulties, however, in providing such roofs. Firstly, they can be extremely expensive and difficult to maintain given the support structures required to ensure rapid and reliable movement of the roof. In addition, the requirement of such roofs is such that they can increase significantly the overall cost of the stadia, given that their additional weight introduces additional structural burdens on the rest of the building. For example, it is usual to use arches, trusses or suchlike to support the roof across its entire span.
The present invention seeks to provide a roof which is retractable, but which can be employed to cover a large area and which has considerably reduced weight in comparison with known retractable roofs.
According to the present invention there is provided a system for operating a retractable roof having at least two movable roof sections, the system comprising:
a first support having a first pulley;
a second support positioned opposite to and across from the first support means and having a second pulley;
a tie member which passes around the first and second pulleys to form an elongate loop having a crossover point between the supports;
wherein the first roof section is supported, in use, by the tie member between the first support and the crossover point and the second roof section is supported, in use, by the tie member between the crossover point and the second support such that, in use, the roof sections move in opposite directions when the tie member is moved.
One of the pulleys may be provided with driving means, such as a motor and gearbox, for moving the tie member and thus operating the roof. The tie member may pass through each support twice to form a double loop arrangement to provide resistance to lateral movement. In this double loop arrangement, the tie member may be connected to each roof section in two places, one of which is a pulley point and the other is a fixed point, that is clamped to the tie member such that the roof section is caused to move with the tie member. The first and second roofs sections may, in use, be attached to the tie member at points equidistant from the cross over point.
Additional pulleys may be provided on each side of the crossover point between the support and the connection of the tie member to the roof section for controlling the path which the tie member takes and thus altering the direction of travel of the roof sections. If the additional pulleys are placed so as to lower the path of the tie member, then the direction of travel of the roof section will be made more convex/less concave. If the additional pulleys are placed so as to raise the path of the tie member, then the direction of travel of the roof section will be made more concave/less convex.
The position of the additional pulley may be controlled by, for example, a hydraulic ram. The ram may also adjust the tension of the tie member so that it is maintained at a substantially constant value to ensure that undue stresses are not placed on the system.
The roof sections may be arranged such that, when they are in the closed position, they are able to lock with one another to provide additional support to one another and to provide a rigid roof structure.
The present invention also provides a retractable roof having one or more systems for operation thereof, and in which the roof sections may be concave or convex.
Preferably, the roof is provided with two systems, each having two roof sections associated therewith, such that a total of four roof sections are provided. The roof may be provided with an outer section which is fixed in place and on which the retractable roof is movably mounted on rails The fixed outer section typically extends over nearly all of the spectator area within the stadium and usually the fixed section extends over approximately half the diameter of the roof. Alternatively, certain projects may require the fixed section to be smaller and thus it may cover only about one third of the roof diameter. In this arrangement, the roof sections may be formed from more than one roof element, such that, in the retracted position, the roof elements are stacked one on top of another, and, in the extended position, the elements are adjacent to each other to form a roof section.
The fixed outer section may be provided with retaining means for preventing the retractable roof sections from being lifted when in the retracted position, such as by a sudden updraft of wind. The retaining means preferably comprises a cable which is attached at one end to the fixed roof section, preferably the underside thereof, or to a ring beam and at the other end is slidably mounted on the underside of the retractable roof.
According to the invention there is also provided a stadium comprising a roof and system of the type described above. Such a stadium may comprise one or more roofs, each of which may have one or more corresponding systems.
Thus the present invention provides a roof which breaks the supporting span of the roof such that arches, trusses and suchlike are not required.